Controller and method

ABSTRACT

A controller for a gas turbine, wherein the gas turbine includes the compressor arranged to operate at a rotational speed n, the combustor and the fuel supply including the first fuel supply and the second fuel supply, wherein the compressor is arranged to provide air to the combustor at a steady state air mass flow rate m ss  and wherein the fuel supply is arranged to supply fuel at a fuel mass flow rate m total  to the combustor. The controller is arranged to, responsive to a load change ΔL to the load L, control the compressor to provide air to the combustor at a new air mass flow rate m TR , wherein the new air mass flow rate m TR  is within a range between a first threshold m LBO  and a second threshold m SUR .

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2019/053576 filed 13 Feb. 2019, and claims the benefitthereof. The International Application claims the benefit of EuropeanApplication No. EP18158433 filed 23 Feb. 2018. All of the applicationsare incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention relates generally to controllers for gas turbines,to gas turbines comprising such controllers and to methods ofcontrolling such gas turbines.

BACKGROUND

Conventional controllers for gas turbines implement relativelyconservative control methods such that the gas turbines are operated atrelatively higher safety margins. These conservative control methodsimpose restrictions on transient events, such as load acceptance andload rejection, such that only relatively small loads may be accepted orrejected.

WO 2015185413 A1 describes a method for determining a fuel split settingvalue utilisable for adjusting a fuel split setting for a combustiondevice, the fuel split setting defining a relation between main fuel andpilot fuel.

EP2104802 B1 describes a method of controlling a fuel split of a pilotfuel flow and a main fuel flow in a gas turbine combustor in case ofload reductions characterised in that the rate of change of fuel demandis monitored and an additional pilot fuel flow is added the amount ofwhich depends on the rate of the change in fuel flow demand.

U.S. Pat. No. 9,822,710 B2 describes a combustion device control unitand a combustion device, e.g. a gas turbine, which determine on thebasis of at least one operating parameter whether the combustion deviceis in a predefined operating stage. In response hereto, there isgenerated a control signal configured for setting a ratio of at leasttwo different input fuel flows to a predetermined value for apredetermined time in case the combustion device is in the predefinedoperating stage.

US 2004/216,462 A1 discloses a gas turbo group having a combustionchamber comprising a catalytic burner stage, a pre-burner stage locatedupstream from the catalytic burner stage, as well as a non-catalyticburner stage located downstream from the catalytic burner stage. Thepre-burner stage serves to always maintain a temperature at the inletinto the catalytic stage that corresponds at least to a minimumtemperature necessary for operating the catalytic burner stage.According to the invention, the gas turbo group is operated so that theburner stage located downstream from the catalytic combustion chamber istaken into operation only when the temperature at the outlet from thecatalytic stage has reached an upper limit in the presence of a maximumcombustion air mass flow.

US 2014/026,587 A1 discloses a method and system for transient operatingof a gas turbine. Operation of the gas turbine the controller determinescommand values for an inlet air mass flow, fuel mass flow, and for awater or steam mass flow. In order to allow fast transient operationwith a stable premix flame at least one command value is dynamicallycompensated to compensate for the different system dynamics of thesupply systems to synchronize the resulting changes in fuel, water,steam, and/or combustion air mass flows, which reach the combustor, sothat the fuel to air ratio stays within the combustible limit.

U.S. Pat. No. 5,896,716 A discloses a rapid acting control system for agas turbine in an electrical system that is adapted to control fuel andair supply to the turbine to prevent flameout condition in the turbineand includes: a turbine control unit having an air supply controllerthat controls the position of a plurality of turbine inlet guide vanes(IGVs) in correspondence with at least one turbine condition signal; aload rejection module coupled to the air supplier controller and to aturbine electrical load sensor so as to generate a transient IGVcorrection signal in correspondence with a sensed turbine electricalload drop condition. A method of operating a gas turbine to maintain theturbine on-line during a loss of load condition includes the steps ofsensing a loss of load condition for the turbine; supplying an inletguide vane correction signal into an air supply controller coupled tocontrol the position of a plurality of turbine IGVs, the IGV correctionsignal being independent of other turbine operating condition signalsapplied to the air supply controller; and adjusting the position of theplurality of IGVs in response to the IGV correction signal to adjust theturbine fuel air mixture in the gas turbine to prevent flameout during aloss of electrical load condition. The method typically further includesthe step of removing the IGV correction signal after a correction timedelay.

WO 00/17577 A1 discloses a unique and useful dynamic control system forthe control of a catalytic combustion system for use on a dynamic plant,preferably, a gas turbine engine. The dynamic control system facilitatesthe replacement of conventional flame combustion systems with catalyticcombustion systems. A method of controlling the catalytic combustionprocess comprises the steps of calculating a mass flow of air introducedinto the combustor, monitoring a flow of fuel to be combusted within thecombustor, monitoring a temperature of the air introduced into thecombustor, calculating an inlet temperature set point based on the massflow and fuel flow, and controlling a pre-burner to heat the air basedon the inlet temperature set point, the mass flow, and the temperatureof the air. Further, the mass flow may be estimated based on ambient airtemperature and pressure, and compressor speed. A catalytic combustiongas turbine system is also presented, the operation of which iscontrolled by a dynamic plant controller which generates a fuel flowrate demand signal to control the flow of fuel to be combusted inresponse to dynamic plant demands.

Hence, there is a need to improve control of gas turbines, for examplecontrol related to transient events, such as load acceptance and loadrejection.

SUMMARY

According to the present disclosure there is provided a method ofcontrolling a gas turbine, a controller for a gas turbine, a gas turbinecomprising such a controller and a tangible non-transientcomputer-readable storage medium as set forth in the appended claims.Other features of the invention will be apparent from the dependentclaims, and the description which follows.

According to a first aspect, there is provided a method of controlling agas turbine arranged to supply a load L, the gas turbine comprising acompressor arranged to operate at a rotational speed n, a combustor anda fuel supply means comprising a first fuel supply means and a secondfuel supply means, wherein the compressor is arranged to provide air tothe combustor at a steady state air mass flow rate {dot over (m)}_(SS)and wherein the fuel supply means is arranged to supply fuel at a fuelmass flow rate m_(total) to the combustor, the method comprising:

responsive to a load change ΔL to the load L, controlling the compressorto provide air to the combustor at a new air mass flow rate {dot over(m)}_(TR), wherein the new air mass flow rate {dot over (m)}_(TR) iswithin a range between a first threshold {dot over (m)}_(LBO) and asecond threshold {dot over (m)}_(SUR).

In this way, the control of the gas turbine is better adapted fortransient events, such as load acceptance and/or load rejection. In thisway, the gas turbine may be better controlled to increase power output,for example more quickly and/or more accurately, during load acceptance,thereby enabling increased loads to be accepted without stalling the gasturbine, for example. In this way, the gas turbine may be bettercontrolled to decrease power output, for example more quickly and/ormore accurately, during load rejection, thereby enabling increased loadsto be rejected without over-speeding, which may cause over-frequency ofelectrical generators, for example. In one example, the method is aclosed control loop method.

It should be understood that the rotational speed n is a non-dimensionalrotational speed n given by:

$\overset{\_}{n} = \frac{{\overset{\_}{n}}_{actual}}{\sqrt{T}}$where n _(actual) is the actual rotational speed of the compressor and Tis the absolute temperature of the air at the compressor inlet.

It should be understood that air mass flow rates {dot over (m)}, forexample the steady state air mass flow rate {dot over (m)}_(SS) and thenew air mass flow rate {dot over (m)}_(TR), are non-dimensional air massflow rates given generally by:

$\overset{.}{\overset{\_}{m}} = {\overset{.}{m} \times \frac{\sqrt{T}}{P}}$where {dot over (m)} is the actual air mass flow rate, T is the absolutetemperature of the air and P is the pressure of the air at thecompressor inlet.

In one example, the first threshold {dot over (m)}_(LBO) is a lean blowout (LBO) limit, corresponding with loss of a burner flame. In oneexample, the second threshold {dot over (m)}_(SUR) is the surge limit,corresponding with surge of the compressor. In one example, the firstthreshold {dot over (m)}_(LBO) and/or the second threshold {dot over(m)}_(SUR) is measured, for example, from the gas turbine. In oneexample, the first threshold {dot over (m)}_(LBO) and/or the secondthreshold {dot over (m)}_(SUR) is included in a real-time model of thegas turbine. In this way, the gas turbine may be controlled to operatecloser to the first threshold {dot over (m)}_(LBO) and/or the secondthreshold {dot over (m)}_(SUR).

In one example, controlling the compressor to provide air to thecombustor at the new air mass flow rate {dot over (m)}_(TR) comprisesdetermining a correction factor CF for the load change ΔL to the load Land adjusting the air mass flow rate {dot over (m)} to the new air massflow rate {dot over (m)}_(TR) based, at least in part, on the determinedcorrection factor CF. In this way, the gas turbine may be controlledpre-emptively and/or reactively to transient events.

In one example, determining the correction factor CF comprisescalculating the correction factor CF according to:

${CF} = \frac{{\overset{.}{\overset{\_}{m}}}_{TR} - {\overset{.}{\overset{\_}{m}}}_{SUR}}{{\overset{.}{\overset{\_}{m}}}_{SS} - {\overset{.}{\overset{\_}{m}}}_{SUR}}$if the load change ΔL to the load L is positive.

In one example, determining the correction factor CF comprisescalculating the correction factor CF according to:

${CF} = \frac{{\overset{.}{\overset{\_}{m}}}_{TR} - {\overset{.}{\overset{\_}{m}}}_{SUR}}{{\overset{.}{\overset{\_}{m}}}_{SS} - {\overset{.}{\overset{\_}{m}}}_{SUR}}$if {dot over (m)}_(TR)>({dot over (m)}_(SS)+Ä{dot over (m)}_(HIGH)),wherein Ä{dot over (m)}_(HIGH) is within a range between the steadystate air mass flow rate {dot over (m)}_(SS) and the second threshold{dot over (m)}_(SUR).

In one example, determining the correction factor CF comprisescalculating the correction factor CF according to:

${CF} = \frac{{\overset{.}{\overset{\_}{m}}}_{LEO} - {\overset{.}{\overset{\_}{m}}}_{TR}}{{\overset{.}{\overset{\_}{m}}}_{LEO} - {\overset{.}{\overset{\_}{m}}}_{SS}}$if the load change ΔL to the load L is negative.

In one example, determining the correction factor CF comprisescalculating the correction factor CF according to:

${CF} = \frac{{\overset{.}{\overset{\_}{m}}}_{LEO} - {\overset{.}{\overset{\_}{m}}}_{TR}}{{\overset{.}{\overset{\_}{m}}}_{LEO} - {\overset{.}{\overset{\_}{m}}}_{SS}}$if {dot over (m)}_(TR)<({dot over (m)}_(SS)−Ä{dot over (m)}_(LOW)),wherein Ä{dot over (m)}_(LOW) is within a range between the steady stateair mass flow rate {dot over (m)}_(SS) and the first threshold {dot over(m)}_(LBO).

In one example, controlling air provided to the combustor at the new airmass flow rate {dot over (m)}_(TR) comprises determining a rate ofchange of the rotational speed dn/dt corresponding to the load change ΔLto the load L and adjusting the air mass flow rate {dot over (m)}_(SS)to the new air mass flow rate {dot over (m)}_(TR) based, at least inpart, on the determined correction factor CF and the determined rate ofchange of the rotational speed dn/dt.

In one example, controlling air provided to the combustor at the new airmass flow rate {dot over (m)}_(TR) comprises adjusting the steady stateair mass flow rate {dot over (m)}_(SS) to the new air mass flow rate{dot over (m)}_(TR) based, at least in part, on a product of thedetermined correction factor CF and the determined rate of change of therotational speed dn/dt.

In one example, controlling air provided to the combustor at the new airmass flow rate {dot over (m)}_(TR) comprises adjusting the steady stateair mass flow rate {dot over (m)}_(SS) to the new air mass flow rate{dot over (m)}_(TR) based on a sum of the determined rate of change ofthe rotational speed dn/dt and the product of the determined correctionfactor CF and the determined rate of change of the rotational speeddn/dt.

In one example, the method comprises: responsive to the load change ΔLto the load L, controlling the fuel supply means to supply a proportionZ of the fuel mass flow rate m_(total) as a fuel mass flow rate {dotover (m)}_(fuel_pilot) via the first fuel supply means based, at leastin part, on a combustor mass flow rate {dot over (m)}_(T).

In one example, controlling the proportion Z of the fuel mass flow ratem_(total) as the fuel mass flow rate {dot over (m)}_(fuel_pilot)supplied via the first fuel supply means is based, at least in part, ona previous combustor mass flow rate {dot over (m)}_(T-1) supplied viathe first fuel supply means in a previous time step T−1.

In one example, controlling the proportion Z of the fuel mass flow ratem_(total) as the fuel mass flow rate {dot over (m)}_(fuel_pilot)supplied via the first fuel supply means is based, at least in part, onthe previous combustor mass flow rate {dot over (m)}_(T-1) supplied viathe first fuel supply means in the previous time step T−1, wherein theprevious combustor mass flow rate {dot over (m)}_(T-1) is provided froma set thereof. In one example, the set is measured, for example, fromthe gas turbine. In one example, set is included in a real-time model ofthe gas turbine. In this way, the gas turbine may be controlled tooperate closer to the set.

According to a second aspect, there is provided a controller for a gasturbine, the gas turbine comprising a compressor arranged to operate ata rotational speed n, a combustor and a fuel supply means comprising afirst fuel supply means and a second fuel supply means, wherein thecompressor is arranged to provide air to the combustor at a steady stateair mass flow rate {dot over (m)}_(SS) and wherein the fuel supply meansis arranged to supply fuel at a fuel mass flow rate m_(total) to thecombustor, wherein the controller is arranged to: responsive to a loadchange ΔL to the load L, control the compressor to provide air to thecombustor at a new air mass flow rate {dot over (m)}_(TR), wherein thenew air mass flow rate {dot over (m)}_(TR) is within a range between afirst threshold {dot over (m)}_(LBO) and a second threshold {dot over(m)}_(SUR).

According to a third aspect, there is provided a method of controlling agas turbine arranged to supply a load L, the gas turbine comprising acompressor arranged to operate at a rotational speed n, a combustor anda fuel supply means comprising a first fuel supply means and a secondfuel supply means, wherein the compressor is arranged to provide air tothe combustor at a steady state air mass flow rate {dot over (m)}_(SS)and wherein the fuel supply means is arranged to supply fuel at a fuelmass flow rate m_(total) to the combustor, the method comprising:responsive to the load change ΔL to the load L, controlling the fuelsupply means to supply a proportion Z of the fuel mass flow ratem_(total) as a fuel mass flow rate {dot over (m)}_(fuel_pilot) via thefirst fuel supply means based, at least in part, on a combustor massflow rate {dot over (m)}_(t).

In this way, the control of the gas turbine is better adapted fortransient events, such as load acceptance and/or load rejection. In thisway, the gas turbine may be better controlled to increase power output,for example more quickly and/or more accurately, during load acceptance,thereby enabling increased loads to be accepted without loss of a pilotflame of the combustor, for example. In this way, the gas turbine may bebetter controlled to decrease power output, for example more quicklyand/or more accurately, during load rejection, thereby enablingincreased loads to be rejected without overheating of a burner of thecombustor. In this way, control of the gas turbine is better adapted fortransient events, reducing likelihood of trips, faults, damage and/ordeterioration.

In one example, the method is a closed control loop method. This methodcomprises an adaptive closed-loop transient scheduling of total fueldemand to control acceleration and/or deceleration of the compressorbased on model-based control parameter(s) such as compressor air massflow and predetermined operational limits like compressor surge andcombustor Lean Blow Out Limit. This contributes to more robust gasturbine engine operation during transient events such as load acceptanceand load rejection.

In one example, controlling the proportion Z of the fuel mass flow ratem_(total) as the fuel mass flow rate {dot over (m)}_(fuel_pilot) u esupplied via the first fuel supply means is based, at least in part, ona previous combustor mass flow rate {dot over (m)}_(t-1) supplied viathe first fuel supply means and/or the compressor in a previous timestep t−1. In this way, the gas turbine may be controlled based, at leastin part, on previous operating conditions.

In one example, controlling the proportion Z of the fuel mass flow ratem_(total) as the fuel mass flow rate {dot over (m)}_(fuel_pilot)supplied via the first fuel supply means is based, at least in part, onthe previous combustor mass flow rate {dot over (m)}_(T-1) supplied viathe first fuel supply means and/or the compressor in the previous timestep t−1, wherein the previous combustor mass flow rate {dot over(m)}_(t-1) is provided from a set thereof.

In one example, the proportion Z of the fuel mass flow rate m_(total) asthe fuel mass flow rate {dot over (m)}_(fuel_pilot) supplied via thefirst fuel supply means is within a range between a first pilotthreshold {dot over (m)}_(LBO) and a second pilot threshold {dot over(m)}_(TT).

In one example, the first pilot threshold {dot over (m)}_(LBO)corresponds with loss of a pilot flame of the combustor.

In one example, the second pilot threshold {dot over (m)}_(TT)corresponds with overheating of a burner of the combustor.

In one example, the first pilot threshold {dot over (m)}_(LBO) ispre-determined for the gas turbine.

In one example, the second pilot threshold {dot over (m)}_(TT) ispre-determined for the gas turbine.

In one example, the proportion Z of the fuel mass flow rate m_(total) asthe fuel mass flow rate {dot over (m)}_(fuel_pilot) supplied via thefirst fuel supply means is below the first pilot threshold {dot over(m)}_(LBO) to for at most a predetermined first duration.

In one example, the proportion Z of the fuel mass flow rate m_(total) asthe fuel mass flow rate {dot over (m)}_(fuel_pilot) supplied via thefirst fuel supply means is above the second pilot threshold {dot over(m)}_(TT) for at most a predetermined second duration.

In one example, controlling the proportion Z of the fuel mass flow ratem_(total) as the fuel mass flow rate {dot over (m)}_(fuel_pilot)supplied via the first fuel supply means comprises decreasing theproportion Z if the load change ΔL to the load L is positive.

In one example, controlling the proportion Z of the fuel mass flow ratem_(total) as the fuel mass flow rate {dot over (m)}_(fuel_pilot)supplied via the first fuel supply means comprises decreasing theproportion Z if the load change ΔL to the load L is negative.

According to a fourth aspect, there is provided controller for a gasturbine, the gas turbine comprising a compressor arranged to operate ata rotational speed n, a combustor and a fuel supply means comprising afirst fuel supply means and a second fuel supply means, wherein thecompressor is arranged to provide air to the combustor at a steady stateair mass flow rate {dot over (m)}_(SS) and wherein the fuel supply meansis arranged to supply fuel at a fuel mass flow rate m_(total) to thecombustor, wherein the controller is arranged to: responsive to a loadchange ΔL to the load L, control the fuel supply means to supply aproportion Z of the fuel mass flow rate m_(total) as a fuel mass flowrate {dot over (m)}_(fuel_pilot) via the first fuel supply means based,at least in part, on a combustor mass flow rate {dot over (m)}_(t).

According to a fifth aspect, there is provided a gas turbine comprisinga compressor arranged to operate at a rotational speed n, a combustorand a fuel supply means comprising a first fuel supply means and asecond fuel supply means, wherein the compressor is arranged to provideair to the combustor at a steady state air mass flow rate {dot over(m)}_(SS) and wherein the fuel supply means is arranged to supply fuelat a fuel mass flow rate m_(total) to the combustor, wherein the gasturbine comprises a controller according to the second aspect and/or thefourth aspect.

According to a sixth aspect, there is provided a tangible non-transientcomputer-readable storage medium is provided having recorded thereoninstructions which when implemented by a controller for a gas turbine,the gas turbine comprising a compressor arranged to operate at arotational speed n, a combustor and a fuel supply means comprising afirst fuel supply means and a second fuel supply means, wherein thecompressor is arranged to provide air to the combustor at a steady stateair mass flow rate {dot over (m)}_(SS) and wherein the fuel supply meansis arranged to supply fuel at a fuel mass flow rate m_(total) to thecombustor, cause the controller to perform a method of controlling thegas turbine, the method according to the first aspect and/or the thirdaspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present disclosure will now be described with referenceto the accompanying drawings, in which:

FIG. 1 shows a schematic view of a gas turbine of a type that may beused according to an exemplary embodiment;

FIG. 2 shows a schematic view of the gas turbine of FIG. 1 , in moredetail;

FIG. 3 shows a schematic view of the gas turbine of FIG. 1 , in moredetail;

FIG. 4 shows a schematic view of the gas turbine of FIG. 1 , in moredetail;

FIG. 5 shows a schematic view of the gas turbine of FIG. 1 , in moredetail;

FIG. 6 shows a schematic view of a controller according to an exemplaryembodiment;

FIG. 7 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment;

FIG. 8 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment;

FIG. 9 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment;

FIG. 10 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment;

FIG. 11 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment;

FIG. 12 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment;

FIG. 13 shows a schematic view of a controller according to an exemplaryembodiment;

FIG. 14 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment;

FIG. 15 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment;

FIG. 16 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment; and

FIG. 17 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment.

DETAILED DESCRIPTION

FIG. 1 shows a schematic view of a gas turbine 100 of a type that may beused according to an exemplary embodiment. The gas turbine 100 comprisesa compressor 101, a combustor 102, a compressor turbine 103, a powerturbine 104, and an interduct 105.

The gas turbine 100 comprises a gas generator device which is adaptedfor generating pressurized working fluid. The gas generator devicecomprises the compressor 101, the combustor 102 and the compressorturbine 103. A working fluid, such as air, is injected into thecompressor 101. The compressor 101 pressurizes the working fluid.

The arrows in FIG. 1 show the flow direction of the working fluid.Downstream of the compressor 101, fuel is injected into the combustor102. The working fluid, i.e. a part of the working fluid, is mixed withthe fuel and is burned. The combustor 102 generates pressurized, highenergized working fluid which drives the compressor turbine 103 suchthat mechanical energy is generated for driving the compressor 101,respectively.

The hot pressurized, high energized working fluid is guided through aninterduct 105 to the power turbine 104. The pressurized hot workingfluid drives the power turbine 104 for generating torque.

FIG. 2 shows a schematic view of the gas turbine 100 of FIG. 1 , in moredetail. Particularly, FIG. 2 shows schematically the compressor 101, thecombustor 102 and the compressor turbine 103 of the gas turbine 100 asshown in FIG. 1 in more detail.

The terms upstream and downstream refer to the flow direction of theairflow and/or working gas flow through the engine unless otherwisestated. The terms forward and rearward refer to the general flow of gasthrough the engine. The terms axial, radial and circumferential are madewith reference to a rotational axis 20 of the engine.

The gas turbine 100 comprises, in flow series, an inlet 12, thecompressor 101, the combustor 102 and the compressor turbine 103 whichare generally arranged in flow series and generally in the direction ofa longitudinal or rotational axis 20. The gas turbine 100 furthercomprises a shaft 22 which is rotatable about the rotational axis 20 andwhich extends longitudinally through the gas turbine 100. The shaft 22drivingly connects the compressor turbine 103 to the compressor 101.

In operation of the gas turbine 100, air 24, which is taken in throughthe air inlet 12 is compressed by the compressor 101 and delivered tothe combustor 102 comprising a burner section 16. The burner section 16comprises a burner plenum 26, one or more combustion chambers 28 definedby a double wall can 27 and at least one burner 30 fixed to eachcombustion chamber 28. The combustion chambers 28 and the burners 30 arelocated inside the burner plenum 26. The compressed air passing throughthe compressor 101 enters a diffuser 32 and is discharged from thediffuser 32 into the burner plenum 26 from where a portion of the airenters the burner 30 and is mixed with a gaseous or liquid fuel. Theair/fuel mixture is then burned and the combustion gas 34 or working gasfrom the combustion is channelled via a transition duct 35 to thecompressor turbine 103.

The compressor turbine 103 comprises a number of blade carrying discs 36attached to the shaft 22. In the present example, two discs 36 eachcarry an annular array of turbine blades 38. However, the number ofblade carrying discs could be different, i.e. only one disc or more thantwo discs. In addition, guiding vanes 40, which are fixed to a stator 42of the gas turbine 100, are disposed between the turbine blades 38.Between the exit of the combustion chamber 28 and the leading turbineblades 38 inlet guiding vanes 44 are provided.

The combustion gas from the combustion chamber 28 enters the compressorturbine 103 and drives the turbine blades 38 which in turn rotates theshaft 22. The guiding vanes 40, 44 serve to optimise the angle of thecombustion or working gas on to the turbine blades 38. The compressor101 comprises an axial series of guide vane stages 46 and rotor bladestages 48.

FIG. 3 shows a schematic view of the gas turbine of FIG. 1 , in moredetail. Particularly, FIG. 3 shows a part of the combustion chamber 28,in more detail.

FIG. 4 shows a schematic view of the gas turbine of FIG. 1 , in moredetail. Particularly, FIG. 4 shows a section of the combustion chamber28 along a line III-III shown in FIG. 3 .

The combustion chamber 28 is in four parts: a front-end part 120, aswirler part 121, a burner pre-chamber part 122 and a combustion volume123. Main fuel is introduced into the swirler 121 by way of thefront-end part 120 through a conduit 124, while pilot fuel enters theburner space through a conduit 125 having at its end a pilot-fuel nozzle129. The main and pilot fuel-flows are derived from a fuel-split valve126, which is fed with a fuel supply means 127 representing the totalfuel supply to the combustion chamber 123. The fuel supply means 127comprises thus a main or first fuel supply means and a pilot or secondfuel supply means. The main fuel flow enters the swirler 121 through aset of main-fuel nozzles (or injector) 128, from where it is guidedalong swirler vanes 130, being mixed with incoming compressed air in theprocess. The fuel may be gaseous fuel or liquid fuel. The resultingair/fuel mixture maintains a burner flame 30. The hot air from thisburner flame 30 enters the combustion volume 123. A gas turbine willoften comprise a number of such combustion chambers 28, in which casethe main and pilot fuel-flow distribution will usually be as shown inFIG. 5 .

FIG. 5 shows a schematic view of the gas turbine of FIG. 1 , in moredetail. Particularly, FIG. 5 shows the main and pilot fuel-flowdistribution for 1, 2, . . . N combustion chambers 28. The main andpilot fuel-flows are derived from the fuel-split valve 126, which is fedwith the fuel supply means 127 representing the total fuel supply to the1, 2, . . . N combustion chambers 28. The fuel supply means 127comprises thus the main or first fuel supply means and the pilot orsecond fuel supply means.

FIG. 6 shows a schematic view of a controller 600 according to anexemplary embodiment. Particularly, FIG. 6 shows a schematic view of thecontroller 600 communicatively coupled to the gas turbine 100.

The controller 600 is for the gas turbine 100. The gas turbine 100comprises the compressor 101 arranged to operate at a rotational speedn, the combustor 102 and the fuel supply means 127 comprising the firstfuel supply means and the second fuel supply means, wherein thecompressor 101 is arranged to provide air to the combustor 102 at asteady state air mass flow rate {dot over (m)}_(SS) and wherein the fuelsupply means 127 is arranged to supply fuel at a fuel mass flow ratem_(total) to the combustor 102. The controller 600 is arranged to,responsive to a load change ΔL to the load L, control the compressor 101to provide air to the combustor 102 at a new air mass flow rate {dotover (m)}_(TR), wherein the new air mass flow rate {dot over (m)}_(TR)is within a range between a first threshold {dot over (m)}_(LBO) and asecond threshold {dot over (m)}_(SUR).

In this example, the controller 600 comprises a real-time model unit610, a correction factor determination unit 620, anacceleration/deceleration schedule unit 630, a multiplication unit 640,an acceleration/deceleration determination unit 650, a summation unit660, a Proportional Integral (PI) controller unit 670 and a selectorunit 680. Other arrangements are possible.

In one example, the real-time model unit 610 is arranged to determine anestimate of the new air mass flow rate {dot over (m)}_(TR). In oneexample, the real-time model unit 610 is arranged to determine theestimate of the new air mass flow rate {dot over (m)}_(TR) based, atleast in part, on a real-time model of the gas turbine 100. In oneexample, the real-time model unit 610 is arranged to determine theestimate of the new air mass flow rate {dot over (m)}_(TR) based, atleast in part, on the rotational speed n. In one example, the real-timemodel unit 610 is arranged to receive the rotational speed n from thegas turbine 100. In one example, the real-time model unit 610 isarranged to provide the determined estimate of the new air mass flowrate {dot over (m)}_(TR) to the correction factor determination unit620.

In one example, the real-time model unit 610 comprises a real-time (alsoknown as a dynamic) model of the gas turbine 100 describedmathematically by a set of nonlinear differential equations:{dot over (x)}=f _(x)(x,h,u,v)where the distributed aero-thermodynamic, mechanical and electricalprocesses are included in a state coordinate vector {dot over (x)}. Forn state variables, n sets of the above equation may be written.Controls, u, operating conditions, v, and health parameters, h, arequantities which may be distinguished by measurement and/ormanipulation.

Measurements (also known as sensed parameters) may be taken on variousquantities in the gas turbine 100. These sensed parameters may berelated to the states, inputs and parameters according to the generalalgebraic expression:y=g _(y)(x,h,u,v)

Where, in general, vector y comprises measurable and non-measurableparameters. These above equations for the state coordinate vector {dotover (x)} and the vector y may be general enough to provide a startingpoint to describe the gas turbine 100 with respect to control design andstate estimation.

After an accurate model is developed for the generic baseline, this gasturbine model may be expanded to include data representing thedeteriorated gas turbine 100 (i.e. following use of the gas turbine 100,for example following commissioning and/or extended use thereof).Deterioration effects may include efficiency changes, area changes,pressure drops, as well as flow changes and disturbances due to bleedeffects, for example. Typically, the two quantities of capacity andefficiency may be used to model changes in operation of the gas turbine100 resulting in decreased energy conversion efficiency or componentflow characteristics.

In one example, the real-time model is as described in WO 2015/117791and/or WO 2017/198528.

In one example, the controller 600 is arranged to, responsive to theload change ΔL to the load L, control the compressor 101 to provide airto the combustor 102 at the new air mass flow rate {dot over (m)}_(TR)by determining a correction factor CF for the load change ΔL to the loadL and adjusting the air mass flow rate {dot over (m)} to the new airmass flow rate {dot over (m)}_(TR) based, at least in part, on thedetermined correction factor CF. In one example, the correction factorCF comprises and/or is an acceleration correction factor ACF. In oneexample, the correction factor CF comprises and/or is a decelerationcorrection factor DCF.

In one example, the correction factor determination unit 620 is arrangedto determine the correction factor CF for the load change ΔL to the loadL. In one example, the correction factor determination unit 620 isarranged to determine the correction factor CF for the load change ΔL tothe load L based, at least in part, on the determined estimate of thenew air mass flow rate {dot over (m)}_(TR) provided by the real-timemodel unit 610. In one example, the correction factor determination unit620 is arranged to determine the correction factor CF based, at least inpart, on the rotational speed n. In one example, the correction factordetermination unit 620 is arranged to determine the correction factor CFas described with reference to FIGS. 8, 9 and 11 . In one example, thecorrection factor determination unit 620 is arranged to receive therotational speed n from the gas turbine 100. In one example, thecorrection factor determination unit 620 is arranged to provide thedetermined correction factor CF for the load change ΔL to the load L tothe multiplication unit 640.

In one example, the correction factor determination unit 620 is arrangedto determine the correction factor CF by calculating the correctionfactor CF according to:

${CF} = \frac{{\overset{.}{\overset{\_}{m}}}_{TR} - {\overset{.}{\overset{\_}{m}}}_{SUR}}{{\overset{.}{\overset{\_}{m}}}_{SS} - {\overset{.}{\overset{\_}{m}}}_{SUR}}$if the load change ΔL to the load L is positive. This corresponds toacceleration scheduling during load acceptance i.e. the correctionfactor CF is an acceleration correction factor ACF.

Particularly, there are two special cases to consider if the load changeΔL to the load L is positive.

In the first special case, further acceleration is not possible:CF=ACF=0 for {dot over ( m )}_(TR)={dot over ( m )}_(SUR)−surge limit atn _(K)

In the second special case, free acceleration is possible:CF=ACF=1 for {dot over ( m )}_(TR)={dot over ( m )}_(SS)−running pointat n _(K)

In one example, the correction factor determination unit 620 is arrangedto determine the correction factor CF by calculating the correctionfactor CF according to:

${CF} = \frac{{\overset{.}{\overset{\_}{m}}}_{TR} - {\overset{.}{\overset{\_}{m}}}_{SUR}}{{\overset{.}{\overset{\_}{m}}}_{SS} - {\overset{.}{\overset{\_}{m}}}_{SUR}}$if {dot over (m)}_(TR)>({dot over (m)}_(SS)+Ä{dot over (m)}_(HIGH)),wherein Ä{dot over (m)}_(HIGH) is within a range between the steadystate air mass flow rate {dot over (m)}_(SS) and the second threshold{dot over (m)}_(SUR).

In one example, the correction factor determination unit 620 is arrangedto determine the correction factor CF by calculating the correctionfactor CF according to:

${CF} = \frac{{\overset{.}{\overset{\_}{m}}}_{LEO} - {\overset{.}{\overset{\_}{m}}}_{TR}}{{\overset{.}{\overset{\_}{m}}}_{LEO} - {\overset{.}{\overset{\_}{m}}}_{SS}}$if the load change ΔL to the load L is negative. This corresponds todeceleration scheduling during load rejection i.e. the correction factorCF is a deceleration correction factor DCF.

Particularly, there are two special cases to consider if the load changeΔL to the load L is negative.

In the first special case, further deceleration is not possible:CF=DCF=0 for {dot over ( m )}_(TR)={dot over ( m )}_(LBO)−LBO limit at n_(K)

In the second special case, free deceleration is possible:CF=DCF=1 for {dot over ( m )}_(TR)={dot over ( m )}_(SS)−running pointat n _(K)

In one example, the correction factor determination unit 620 is arrangedto determine the correction factor CF by calculating the correctionfactor CF according to:

${CF} = \frac{{\overset{.}{\overset{\_}{m}}}_{LEO} - {\overset{.}{\overset{\_}{m}}}_{TR}}{{\overset{.}{\overset{\_}{m}}}_{LEO} - {\overset{.}{\overset{\_}{m}}}_{SS}}$if {dot over (m)}_(TR)<({dot over (m)}_(SS)−Ä{dot over (m)}_(LOW)),wherein Ä{dot over (m)}_(LOW) is within a range between the steady stateair mass flow rate {dot over (m)}_(SS) and the first threshold {dot over(m)}_(LBO).

In one example, the controller 600 is arranged to, responsive to theload change ΔL to the load L, control the compressor 101 to provide airto the combustor 102 at the new air mass flow rate {dot over (m)}_(TR)by determining a rate of change of the rotational speed dn/dtcorresponding to the load change ΔL to the load L and adjusting the airmass flow rate {dot over (m)}_(SS) to the new air mass flow rate {dotover (m)}_(TR) based, at least in part, on the determined correctionfactor CF and the determined rate of change of the rotational speeddn/dt.

In one example, the acceleration/deceleration schedule unit 630 isarranged to determine the rate of change of the rotational speed dn/dtcorresponding to the load change ΔL to the load L. In one example, theacceleration/deceleration schedule unit 630 is arranged to determine therate of change of the rotational speed dn/dt corresponding to the loadchange ΔL to the load L as a function of the rotational speed n, forexample, as described below with reference to FIGS. 10 and/or 12 . Inone example, this rate of change comprises and/or is an estimatedacceleration/deceleration demand of the compressor 101. In one example,the acceleration/deceleration schedule unit 630 is arranged to receivethe rotational speed n from the gas turbine 100. In one example, theacceleration/deceleration schedule unit 630 is arranged provide thedetermined rate of change of the rotational speed dn/dt, for example asthe estimated acceleration/deceleration demand of the compressor 101, tothe multiplication unit 640.

In one example, the controller 600 is arranged to control the compressor101 to provide air to the combustor 102 at the new air mass flow rate{dot over (m)}_(TR) by adjusting, for example limiting, the air massflow rate to the new air mass flow rate {dot over (m)}_(TR) based, atleast in part, on a product of the determined correction factor CF andthe determined rate of change of the rotational speed dn/dt.

In one example, the multiplication unit 640 is arranged to multiply(i.e. calculate the product of) the determined correction factor CFprovided by the correction factor determination unit 620 and theestimated acceleration/deceleration demand of the compressor 101provided by the acceleration/deceleration schedule unit 630, therebyproviding a corrected acceleration/deceleration demand of the compressor101. In one example, the multiplication unit 640 is arranged to providethe product of the determined correction factor CF and the determinedrate of change of the rotational speed dn/dt to the summation unit 660.

In one example, the controller 600 is arranged to control the compressor101 to provide air to the combustor 102 at the new fuel mass flow rate{dot over (m)}_(TR) by adjusting, for example limiting, the air massflow rate to the new air mass flow rate {dot over (m)}_(TR) based on asum of the determined rate of change of the rotational speed dn/dt andthe product of the determined correction factor CF and the determinedrate of change of the rotational speed dn/dt.

In one example, the acceleration/deceleration determination unit 650 isarranged to determine the rate of change of the rotational speed dn/dtcorresponding to the load change ΔL to the load L based on the receivedrotational speed n (i.e. an actual value rather than an estimate, forexample). In one example, the acceleration/deceleration determinationunit 650 is arranged to receive the rotational speed n from the gasturbine 100. In one example, the acceleration/deceleration determinationunit 650 is arranged to provide the determined rate of change of therotational speed dn/dt to the summation unit 660.

In one example, the summation unit 660 is arranged to sum the determinedrate of change of the rotational speed dn/dt provided by theacceleration/deceleration determination unit 650 and the product of thedetermined correction factor CF and the determined rate of change of therotational speed dn/dt (i.e. the corrected acceleration/decelerationdemand of the compressor 101) provided by the multiplication unit 640,thereby providing an acceleration/deceleration error of the compressor101 as a difference between the corrected acceleration/decelerationdemand and the actual value provided by the acceleration/decelerationdetermination unit 650. In one example, the summation unit 660 isarranged to provide this sum (i.e. the acceleration/deceleration errorof the compressor 101) to the PI controller 670.

In one example, the controller 600 is arranged to, responsive to theload change ΔL to the load L, control the compressor 101 to provide airto the combustor 102 at the new air mass flow rate {dot over (m)}_(TR)determined from the sum of the determined rate of change of therotational speed dn/dt and the product of the determined correctionfactor CF and the determined rate of change of the rotational speeddn/dt.

In one example, the controller 600 is arranged to, responsive to theload change ΔL to the load L, control the fuel supply means 127 tosupply fuel at the fuel mass flow rate m_(total) to the combustor 102.In one example, the controller 600 is arranged to determine the fuelmass flow rate m_(total) corresponding with the new air mass flow rate{dot over (m)}_(TR).

In one example, the PI controller 670 is arranged to determine the newair mass flow rate {dot over (m)}_(TR) based, at least in part, on thesum, provided by the summation unit 660, of the determined rate ofchange of the rotational speed dn/dt and the product of the determinedcorrection factor CF and the determined rate of change of the rotationalspeed dn/dt (i.e. on the acceleration/deceleration error of thecompressor 101). In one example, the PI controller 670 is arranged toprovide the determined new total fuel mass flow rate m_(total) to theselector 680.

In one example, the PI controller 670 is arranged to determine the fuelmass flow rate m_(total) to be supplied by the fuel supply means 127 tothe combustor 102 based, at least in part, on the sum, provided by thesummation unit 660, of the determined rate of change of the rotationalspeed dn/dt and the product of the determined correction factor CF andthe determined rate of change of the rotational speed dn/dt (i.e. on theacceleration/deceleration error of the compressor 101). In one example,the PI controller 670 is arranged to provide the determined fuel massflow rate m_(total) to the selector 680.

In one example, the selector 680 is arranged to provide the determinednew total fuel mass flow rate m_(total) to the gas turbine 100, forexample to the compressor 101, thereby controlling the gas turbine 100according to the determined new air mass flow rate {dot over (m)}_(TR).In one example, the selector 680 is arranged to provide the determinednew total fuel mass flow rate m_(total) to the real-time model unit 610,thereby feeding this value back into the real-time model.

In one example, the selector 680 is arranged to provide the determinedfuel mass flow rate m_(total) to the gas turbine 100, for example to thefuel supply means 127, thereby controlling the gas turbine 100 accordingto the determined fuel mass flow rate m_(total). In one example, theselector 680 is arranged to provide the determined fuel mass flow ratem_(total) to the real-time model unit 610, thereby feeding this valueback into the real-time model.

At S601, the real-time model unit 610 receives the rotational speed nfrom the gas turbine 100. More generally, at S601, the real-time modelunit 610 receives all available measurements from the gas turbine 100,for example speeds, pressures and/or temperatures at different enginestations.

At S602, the real-time model unit 610 determines the estimate of the newair mass flow rate {dot over (m)}_(TR) based, at least in part, on thereceived rotational speed n, as described above, and provides theestimate of the new air mass flow rate {dot over (m)}_(TR) to thecorrection factor determination unit 620.

At S603, the correction factor determination unit 620 receives therotational speed n from the gas turbine 100.

At S604, the correction factor determination unit 620 determines thecorrection factor CF based, at least in part, on the received rotationalspeed n and the estimate of the new air mass flow rate {dot over(m)}_(TR) provided by the real-time model unit 610, as described above,and provides the determined correction factor CF to the multiplicationunit 640.

At S605, the acceleration/deceleration schedule unit 630 receives therotational speed n from the gas turbine 100.

At S606, the acceleration/deceleration schedule unit 630 determines therate of change of the rotational speed dn/dt corresponding to the loadchange ΔL to the load L as a function of the received rotational speed nas an estimated acceleration/deceleration demand of the compressor 101and provides an allowable, for example acceptable, permissible,permitted, tolerable or sustainable, acceleration/deceleration demand tothe multiplication unit 640.

At S607, the multiplication unit 640 multiplies (i.e. calculates theproduct of) the determined correction factor CF provided by thecorrection factor determination unit 620 and the allowableacceleration/deceleration demand of the compressor 101 provided by theacceleration/deceleration schedule unit 630, thereby providing thecorrected allowable acceleration/deceleration demand of the compressor101. The multiplication unit 640 provides the corrected allowableacceleration/deceleration demand of the compressor 101 to the summationunit 660.

At S608, the acceleration/deceleration determination unit 650 receivesthe rotational speed n from the gas turbine 100.

At S609, the acceleration/deceleration determination unit 650 determinesthe rate of change of the rotational speed dn/dt corresponding to theload change ΔL to the load L based on the received rotational speed n(i.e. an actual value rather than an estimate, for example) and providesthe determined rate of change of the rotational speed dn/dt to thesummation unit 660.

At S610, the summation unit 660 sums the determined rate of change ofthe rotational speed dn/dt provided by the acceleration/decelerationdetermination unit 650 and the corrected acceleration/decelerationdemand of the compressor 101, thereby providing anacceleration/deceleration error of the compressor 101 as a differencebetween the corrected acceleration/deceleration demand and the actualvalue provided by the acceleration/deceleration determination unit 650.The summation unit 660 provides this acceleration/deceleration error ofthe compressor 101 to the PI controller 670.

At S611, the PI controller 670 determines the new fuel mass flow ratem_(total) based, at least in part, on the acceleration/decelerationerror of the compressor 101, as described above. In this example, the PIcontroller 670 determines the fuel mass flow rate m_(total) to besupplied by the fuel supply means 127 to the combustor 102. The PIcontroller 670 provides the fuel mass flow rate m_(total) to theselector 680.

At S612, the selector 680 provides the determined new fuel mass flowrate to the gas turbine 100, thereby controlling the gas turbine 100according to the determined new air mass flow rate {dot over (m)}_(TR).The selector 680 provides the determined fuel mass flow rate m_(total)to the gas turbine 100, for example to the fuel supply means 127,thereby controlling the gas turbine 100 according to the determined fuelmass flow rate m_(total). More generally, at S612, the selector 680 mayprovide the total, the pilot and/or the main fuel demands to the gasturbine 100. The selector 680 may additionally provide other and/or alldemands, for example variable guide vane (VGV) demand and/or blow offvalve (BOV) demand, to the gas turbine 100.

At S613, the selector 680 provides the determined fuel mass flow ratem_(total) to the real-time model unit 610, thereby feeding this valueback into the real-time model. More generally, at S613, the selector 680may provide the total, the pilot and/or the main fuel demands to thereal-time model unit 610. The selector 680 may additionally provideother and/or all demands, for example variable guide vane (VGV) demandand/or blow off valve (BOV) demand, to the real-time model unit 610.

FIG. 7 shows a schematic view of a method of controlling the gas turbine100 according to an exemplary embodiment.

The method is of controlling the gas turbine 100 arranged to supply theload L, the gas turbine 100 comprising the compressor 101 arranged tooperate at a rotational speed n, a combustor 102 and a fuel supply means127 comprising a first fuel supply means and a second fuel supply means,wherein the compressor 101 is arranged to provide air to the combustor102 at a steady state air mass flow rate {dot over (m)}_(SS) and whereinthe fuel supply means 127 is arranged to supply fuel at a fuel mass flowrate m_(total) to the combustor 102.

At S701, responsive to the load change ΔL to the load L, the compressor101 is controlled to provide air to the combustor 102 at the new airmass flow rate {dot over (m)}_(TR), wherein the new air mass flow rate{dot over (m)}_(TR) is within the range between the first threshold {dotover (m)}_(LBO) and the second threshold {dot over (m)}_(SUR).

Optionally, the method comprises repeating S701, for examplesuccessively, periodically, regularly and/or irregularly, responsive tosubsequent load changes ΔL.

The method may include any of the steps described herein.

FIG. 8 shows a schematic view of a method of controlling the gas turbine100 according to an exemplary embodiment. Particularly, FIG. 8 shows apressure map for the gas turbine 100 in which a compressor pressureratio PR is plotted as a function of compressor air mass flow rate {dotover (m)}. The compressor pressure ratio PR is the ratio of thecompressor outlet pressure to the compressor inlet pressure.

The pressure map includes a running line for a steady state air massflow rate {dot over (m)}_(SS), for which the compressor pressure ratioPR is approximately proportional to the compressor air mass flow rate{dot over (m)}. The pressure map includes the first, lower threshold{dot over (m)}_(LBO), which is the lean blow out (LBO) limit,corresponding with loss of the burner flame 30, at lower compressorpressure ratios PR than the running line for the same compressor airmass flow rate {dot over (m)} and which diverges away from the runningline at higher compressor air mass flow rates {dot over (m)}. Thepressure map includes the second, upper threshold {dot over (m)}_(SUR),which is the surge limit, corresponding with surge instability of thecompressor 101, at higher compressor pressure ratios PR than the runningline for the same compressor air mass flow rate {dot over (m)} and whichdiverges away from the running line at higher compressor air mass flowrates {dot over (m)} before converging theretowards. The pressure mapincludes a third threshold Ä{dot over (m)}_(LOW), proximal and parallelto the running line, which is within a range between the steady stateair mass flow rate {dot over (m)}_(SS) (i.e. the running line) and thefirst threshold {dot over (m)}_(LBO). The pressure map includes a fourththreshold Ä{dot over (m)}_(HIGH), proximal and parallel to the runningline, which is within a range between the steady state air mass flowrate {dot over (m)}_(SS) and the second threshold {dot over (m)}_(SUR).The third threshold Ä{dot over (m)}_(LOW) and the fourth threshold Ä{dotover (m)}_(HIGH) correspond with moderate transient events. The pressuremap includes also a plurality, specifically seven in this example, ofapproximately mutually equispaced rotational speed lines, transverse tothe running line, the first threshold {dot over (m)}_(LBO), the secondthreshold {dot over (m)}_(SUR), the third threshold Ä{dot over(m)}_(LOW) and the fourth threshold Ä{dot over (m)}_(HIGH). Threerotational speed lines n _(K−1), n _(K) and n _(K+1), corresponding tothree adjacent rotational speeds n, are labelled.

FIG. 9 shows a schematic view of a method of controlling the gas turbine100 according to an exemplary embodiment. Particularly, FIG. 9 shows anexample of the pressure map, as described with reference to FIG. 8 , foracceleration scheduling during load acceptance due to a positivetransient load change ΔL. As shown by the curved arrow in FIG. 9 ,during load acceptance due to the positive transient load change ΔL, thegas turbine 100 is controlled to move from the initial steady state airmass flow rate {dot over (m)}_(SS) running line to operate at the newair mass flow rate {dot over (m)}_(TR), between the steady state airmass flow rate {dot over (m)}_(SS) and the second threshold {dot over(m)}_(SUR), before returning to operate on the steady state air massflow rate {dot over (m)}_(SS) running line, following load acceptance.In this way, the gas turbine 100 may be controlled to operate closer tothe second threshold {dot over (m)}_(SUR), allowing the gas turbine 100to accept larger positive load changes ΔL without surging.

FIG. 10 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment. Particularly, FIG. 10 shows agraph of a nominal acceleration schedule in which rate of change of therotational speed dn/dt (i.e. acceleration) is plotted as a function ofrotational speed n. The acceleration slowly increases as a function ofrotational speed n and spikes to a maximum of approximately 3,200 at arotational speed n of approximately 13,000 before decreasing at higherspeeds. A normal operating range of the rotational speed n is fromapproximately 11,000 to 13,000, in this example.

FIG. 11 shows a schematic view of a method of controlling the gasturbine 100 according to an exemplary embodiment. Particularly, FIG. 11shows an example of the compressor pressure ratio map, as described withreference to FIG. 8 , for deceleration scheduling during load rejectiondue to a negative transient load change ΔL. As shown by the curved arrowin FIG. 9 , during load rejection due to the negative transient loadchange ΔL, the gas turbine 100 is controlled to move from the initialsteady state air mass flow rate {dot over (m)}_(SS) running line tooperate at the new air mass flow rate {dot over (m)}_(TR), between thesteady state air mass flow rate {dot over (m)}_(SS) and the firstthreshold {dot over (m)}_(LBO), before returning to operate on thesteady state air mass flow rate {dot over (m)}_(SS) running line,following load rejection. In this way, the gas turbine 100 may becontrolled to operate closer to the first threshold {dot over(m)}_(LBO), allowing the gas turbine 100 to accept larger negative loadchanges ΔL without loss of flame.

FIG. 12 shows a schematic view of a method of controlling a gas turbineaccording to an exemplary embodiment. Particularly, FIG. 12 shows agraph of a nominal deceleration schedule in which rate of change of therotational speed dn/dt (i.e. deceleration) is plotted as a function ofrotational speed n. The acceleration is constant as a function ofrotational speed n to approximately 9,000 before decreasing at higherspeeds, in this example.

FIG. 13 shows a schematic view of a controller 700 according to anexemplary embodiment. Particularly, FIG. 13 shows a schematic view ofthe controller 700 communicatively coupled to the gas turbine 100.

In one example, the controller 700 comprises the controller 600 or viceversa.

The controller 700 is for the gas turbine 100. The gas turbine 100comprises the compressor 101 arranged to operate at a rotational speedn, the combustor 102 and the fuel supply means 127 comprising the firstfuel supply means and the second fuel supply means, wherein thecompressor 101 is arranged to provide air to the combustor 102 at asteady state air mass flow rate {dot over (m)}_(SS) and wherein the fuelsupply means 127 is arranged to supply fuel at a fuel mass flow ratem_(total) to the combustor 102. The controller 700 is arranged to,responsive to a load change ΔL to the load L, control the fuel supplymeans 127 to supply a proportion Z of the fuel mass flow rate m_(total)as a fuel mass flow rate {dot over (m)}_(fuel_pilot) via the first fuelsupply means based, at least in part, on a combustor mass flow rate {dotover (m)}_(t).

It should be understood that the combustor mass flow rate {dot over(m)}_(t) is a sum of an air mass flow rate {dot over (m)}(for example,the steady state air mass flow rate {dot over (m)}_(SS) or the new airmass flow rate {dot over (m)}_(TR)) and the fuel mass flow ratem_(total) of the air and of the fuel, respectively, provided to thecombustor 102 by the compressor 101 and supplied by the fuel supplymeans 127, respectively, for a current time step t. The current timestep t may be in a range from 1 ms to 100 ms, preferably from 10 to 50ms.

In this example, the controller 700 comprises a real-time model unit710, a one time step delay unit 790, an acceleration/decelerationschedule unit 730, a multiplication unit 740 and a selector unit 780.Other arrangements are possible.

The real-time model unit 710, the acceleration/deceleration scheduleunit 730, the multiplication unit 740 and/or the selector unit 780 maycomprise and/or be as described above with respect to the real-timemodel unit 610, the acceleration/deceleration schedule unit 630, themultiplication unit 640 and/or the selector unit 680, respectively.

In one example, the real-time model unit 710 is arranged to determinethe combustor mass flow rate m_(t). In one example, the real-time modelunit 710 is arranged to determine the combustor mass flow rate m_(t)based, at least in part, on a real-time model of the gas turbine 100. Inone example, the real-time model unit 710 is arranged to determine thecombustor mass flow rate m_(t) based, at least in part, on therotational speed n. In one example, the real-time model unit 710 isarranged to receive the rotational speed n from the gas turbine 100. Inone example, the real-time model unit 710 is arranged to provide thedetermined combustor mass flow rate m_(t) to the time step delay unit790 and/or to the multiplication unit 740.

In one example, the real-time model unit 710 comprises a real-time (alsoknown as a dynamic) model of the gas turbine 100 describedmathematically by a set of nonlinear differential equations, asdescribed above with respect to the real-time model unit 610:{dot over (x)}=f _(x)(x,h,u,v)where the distributed aero-thermodynamic, mechanical and electricalprocesses are included in a state coordinate vector {dot over (x)}. Forn state variables, n sets of the above equation may be written.Controls, u, operating conditions, v, and health parameters, h, arequantities which may be distinguished by measurement and/ormanipulation.

Measurements (also known as sensed parameters) may be taken on variousquantities in the gas turbine 100. These sensed parameters may berelated to the states, inputs and parameters according to the generalalgebraic expression:y=g _(y)(x,h,u,v)

Where, in general, vector y comprises measurable and non-measurableparameters. These above equations for the state coordinate vector {dotover (x)} and the vector y may be general enough to provide a startingpoint to describe the gas turbine 100 with respect to control design andstate estimation.

After an accurate model is developed for the generic baseline, this gasturbine model may be expanded to include data representing thedeteriorated gas turbine 100 (i.e. following use of the gas turbine 100,for example following commissioning and/or extended use thereof).Deterioration effects may include efficiency changes, area changes,pressure drops, as well as flow changes and disturbances due to bleedeffects, for example. Typically, the two quantities of capacity andefficiency may be used to model changes in operation of the gas turbine100 resulting in decreased energy conversion efficiency or componentflow characteristics.

In one example, the real-time model is as described in WO 2015/117791and/or WO 2017/198528.

In one example, the controller 700 is arranged to control the proportionZ of the fuel mass flow rate m_(total) as the fuel mass flow rate {dotover (m)}_(fuel_pilot) supplied via the first fuel supply means isbased, at least in part, on a previous combustor mass flow rate {dotover (m)}_(t-1) supplied in a previous time step t−1. In one example,the previous time step t−1 is one (i.e. only, a single or exactly one)time step preceding the current time step t.

In one example, the time step delay unit 790 is arranged to determinethe previous combustor mass flow rate {dot over (m)}_(t-1) supplied in aprevious time step t−1, for example corresponding to the determinedcombustor mass flow rate m_(t) for the current time step t received fromthe real-time model unit 710. In one example, the time step delay unit790 is arranged to obtain the previous combustor mass flow rate {dotover (m)}_(t-1), for example from a memory block, for example a look-uptable or a map.

In one example, the controller 700 is arranged to control the proportionZ of the fuel mass flow rate m_(total) as the fuel mass flow rate {dotover (m)}_(fuel_pilot) supplied via the first fuel supply means based,at least in part, on the previous combustor mass flow rate {dot over(m)}_(T-1) supplied in the previous time step t−1, wherein the previouscombustor mass flow rate {dot over (m)}_(t-1) is provided from a setthereof.

In one example, the time step delay unit 790 is arranged to obtain theprevious combustor mass flow rate {dot over (m)}_(t-1) for the previoustime step t−1, for example from a memory block, for example a look-uptable or a map. In one example, the time step delay unit 790 is arrangedto provide the combustor mass flow rate {dot over (m)}_(t) to theacceleration/deceleration schedule unit 730 which contains the memoryblock, for example a look-up table or a map.

In one example, the controller 700 is arranged to, responsive to theload change ΔL to the load L, control the fuel supply means 127 tosupply the proportion Z of the fuel mass flow rate m_(total) as the fuelmass flow rate {dot over (m)}_(fuel_pilot) via the first fuel supplymeans based, at least in part, on an estimated acceleration/decelerationfirst fuel (also known as pilot) demand obtained from aacceleration/deceleration schedule as a function of the combustor massflow rate {dot over (m)}_(t-1) for the previous time step t−1, forexample from an acceleration/deceleration schedule thereof. Theestimated acceleration/deceleration first fuel demand may be determinedgenerally from a ratio of the fuel mass flow rate {dot over(m)}_(fuel_pilot) to the combustor mass flow rate {dot over (m)}:

$\frac{{\overset{.}{m}}_{fuel\_ pilot}}{\overset{.}{m}}$

In one example, the acceleration/deceleration schedule unit 730 isarranged to determine the estimated acceleration/deceleration first fueldemand based, at least in part, on the combustor mass flow rate {dotover (m)}_(t-1) for the previous time step t−1 provided by the time stepunit 790. In one example, the acceleration/deceleration schedule unit730 is arranged to determine the estimated acceleration/decelerationfirst fuel demand as a ratio of the fuel mass flow rate {dot over(m)}_(fuel_pilot) to the combustor mass flow rate {dot over (m)}_(t-1)for the previous time step t−1, for example from anacceleration/deceleration schedule thereof. In one example, theacceleration/deceleration schedule unit 730 is arranged to provide theestimated acceleration/deceleration first fuel demand to themultiplication unit 740.

In one example, the multiplication unit 740 is arranged to multiply(i.e. calculate the product of) the combustor mass flow rate {dot over(m)}_(t) for the current time step t provided by the real-time modelunit 710 and the estimated acceleration/deceleration first fuel demandprovided (i.e. determined from the combustor mass flow rate {dot over(m)}_(t-1) for the previous time step t−1) by theacceleration/deceleration schedule unit 730, thereby providing acorrected acceleration/deceleration first fuel demand. The correctedacceleration/deceleration first fuel demand may be thus expressed as:

${\overset{.}{m}}_{fuel\_ pilot} \times \frac{{\overset{.}{m}}_{t}}{{\overset{.}{m}}_{t - 1}}$

In one example, the multiplication unit 740 is arranged to provide thecorrected acceleration/deceleration first fuel demand to the selector780.

In one example, the selector 780 is arranged to provide the correctedacceleration/deceleration first fuel demand to the gas turbine 100, forexample to the fuel supply means 127, thereby controlling the gasturbine 100 according to the corrected acceleration/deceleration firstfuel demand schedule. In one example, the selector 780 is arranged toprovide the corrected acceleration/deceleration first fuel demand to thereal-time model unit 710 (thereby feeding this value back into thereal-time model) and to the gas turbine 100.

In one example, the proportion Z of the fuel mass flow rate m_(total) asthe fuel mass flow rate {dot over (m)}_(fuel_pilot) supplied via thefirst fuel supply means is within a range between a first pilotthreshold {dot over (m)}_(LBO) and a second pilot threshold {dot over(m)}_(TT).

In one example, the first pilot threshold {dot over (m)}_(LBO)corresponds with loss of a pilot flame of the combustor 102.

In one example, the second pilot threshold {dot over (m)}_(TT)corresponds with overheating of a burner of the combustor 102.

In one example, the first pilot threshold {dot over (m)}_(LBO) ispre-determined for the gas turbine 100, for example according to dataobtained therefrom, included in the real-time model and/or in theacceleration/deceleration schedule, as described above.

In one example, the second pilot threshold {dot over (m)}_(TT) ispre-determined for the gas turbine 100, for example according to dataobtained therefrom, included in the real-time model and/or in theacceleration/deceleration schedule, as described above.

In one example, the proportion Z of the fuel mass flow rate m_(total) asthe fuel mass flow rate {dot over (m)}_(fuel_pilot) supplied via thefirst fuel supply means is below the first pilot threshold {dot over(m)}_(LBO) for at most a predetermined first duration, for example in arange of 1 to 100 time steps, preferably in a range from 1 to 10 timesteps, more preferably in a range from 1 to 5 time steps, for example 3time steps. Temporary deviations below the first pilot threshold {dotover (m)}_(LBO) may be acceptable. The time step may be in a range from1 ms to 100 ms, preferably from 10 to 50 ms.

In one example, the proportion Z of the fuel mass flow rate m_(total) asthe fuel mass flow rate {dot over (m)}_(fuel_pilot) supplied via thefirst fuel supply means is above the second pilot threshold {dot over(m)}_(TT) for at most a predetermined second duration, for example in arange of 1 to 100 time steps, preferably in a range from 1 to 10 timesteps, more preferably in a range from 1 to 5 time steps, for example 3time steps. Temporary deviations above the second pilot threshold {dotover (m)}_(TT) may be acceptable. The time step may be in a range from 1ms to 100 ms, preferably from 10 to 50 ms.

In one example, controlling the proportion Z of the fuel mass flow ratem_(total) as the fuel mass flow rate {dot over (m)}_(fuel_pilot)supplied via the first fuel supply means comprises decreasing theproportion Z if the load change ΔL to the load L is positive.

In one example, controlling the proportion of the fuel mass flow ratem_(total) as the fuel mass flow rate {dot over (m)}_(fuel_pilot)supplied via the first fuel supply means comprises increasing theproportion Z if the load change ΔL to the load L is negative.

At S1301, the real-time model unit 710 receives all availablemeasurements from the gas turbine 100, for example speeds, pressuresand/or temperatures at different engine stations.

At S1302, the real-time model unit 710 determines the combustor massflow rate {dot over (m)}_(t) based, at least in part, the fuel mass flowrate {dot over (m)}_(total) for the current time step t, as describedabove, and provides the combustor mass flow rate m_(t) to the to thetime step unit 790.

At S1303, the time step unit 790 obtains the previous combustor massflow rate {dot over (m)}_(t-1) for the previous time step t−1, forexample from a memory block for example a look-up table or a map, andprovides the previous combustor mass flow rate {dot over (m)}_(t-1) forthe previous time step t−1 to the acceleration/deceleration scheduleunit 730.

At S1304, the acceleration/deceleration schedule unit 730 determines theestimated acceleration/deceleration first fuel demand based, at least inpart, on the combustor mass flow rate {dot over (m)}_(t-1) for theprevious time step t−1 provided by the time step unit 790, from anacceleration/deceleration schedule thereof, and provides the estimatedacceleration/deceleration first fuel demand to the multiplication unit740.

At S1305, the real-time model unit 710 provides the combustor mass flowrate {dot over (m)}_(TR) to the multiplication unit 740.

At S1306, the multiplication unit 740 multiplies (i.e. calculates theproduct of) the combustor mass flow rate {dot over (m)}_(t) for thecurrent time step t provided by the real-time model unit 710 and theestimated acceleration/deceleration first fuel demand provided (i.e.determined from the combustor mass flow rate {dot over (m)}_(t-1) forthe previous time step t−1) by the acceleration/deceleration scheduleunit 730, thereby providing the corrected acceleration/decelerationfirst fuel demand expressed as:

${\overset{.}{m}}_{fuel\_ pilot} \times \frac{{\overset{.}{m}}_{t}}{{\overset{.}{m}}_{t - 1}}$

The multiplication unit 740 provides the correctedacceleration/deceleration first fuel demand to the selector 780.

At S1307, the selector 780 provides the correctedacceleration/deceleration first fuel demand to the gas turbine 100, forexample to the fuel supply means 127, thereby controlling the gasturbine 100 according to the corrected acceleration/deceleration firstfuel demand. More generally, at S1307, the selector 780 may provide thetotal, the pilot and/or the main fuel demands to the gas turbine 100.The selector 780 may additionally provide other and/or all demands, forexample variable guide vane (VGV) demand and/or blow off valve (BOV)demand, to the gas turbine 100.

At S1308, the selector 780 provides the correctedacceleration/deceleration first fuel demand to the real-time model unit710, thereby feeding this value back into the real-time model. Moregenerally, at S1308, the selector 780 may provide the total, the pilotand/or the main fuel demands to the real-time model unit 710. Theselector 780 may additionally provide other and/or all demands, forexample variable guide vane (VGV) demand and/or blow off valve (BOV)demand, to the real-time model unit 710.

FIG. 14 shows a schematic view of a method of controlling the gasturbine 100 according to an exemplary embodiment.

The method is of controlling the gas turbine 100 arranged to supply theload L, the gas turbine 100 comprising the compressor 101 arranged tooperate at a rotational speed n, a combustor 102 and a fuel supply means127 comprising a first fuel supply means and a second fuel supply means,wherein the compressor 101 is arranged to provide air to the combustor102 at a steady state air mass flow rate {dot over (m)}_(SS) and whereinthe fuel supply means 127 is arranged to supply fuel at a fuel mass flowrate m_(total) to the combustor 102.

At S1401, responsive to a load change ΔL to the load L, the fuel supplymeans 127 is controlled to supply the proportion Z of the fuel mass flowrate m_(total) as the fuel mass flow rate {dot over (m)}_(fuel_pilot)via the first fuel supply means based, at least in part, on thecombustor mass flow rate {dot over (m)}_(t).

Optionally, the method comprises repeating S1401, for examplesuccessively, periodically, regularly and/or irregularly, responsive tosubsequent load changes ΔL.

The method may comprise any of the method steps described herein, forexample including as described with respect to FIG. 7 .

FIG. 15 shows a schematic view of a method of controlling the gasturbine 100 according to an exemplary embodiment. Particularly, FIG. 15shows a pilot split map (also known as an acceleration/decelerationpilot demand schedule) for the gas turbine 100 in which a pilot fueldemand split is plotted as a function of combustor mass flow rate {dotover (m)}_(t). The pilot fuel demand split is the ratio of the fuel massflow rate {dot over (m)}_(fuel_pilot) to the combustor mass flow rate{dot over (m)}:

$\frac{PilotDem}{\overset{.}{m}} = \frac{{\overset{.}{m}}_{fuel\_ pilot}}{\overset{.}{m}}$

The pilot split map includes a running line for a steady state combustormass flow rate {dot over (m)}_(t), for which the pilot fuel demand splitis approximately inversely proportional to the combustor mass flow rate{dot over (m)}. The fuel map includes the first, lower pilot threshold{dot over (m)}_(LBO), which is the lean blow out (LBO) limit,corresponding with loss of the pilot flame, at lower pilot fuel demandsplits than the running line for the same combustor mass flow rate {dotover (m)} and which converges towards the running line at highercombustor mass flow rate {dot over (m)}. The pressure map includes thesecond, upper pilot threshold {dot over (m)}_(TT), which is the tiptemperature limit, corresponding with overheating of the burner, athigher pilot fuel demand splits than the running line for the samecombustor mass flow rate {dot over (m)} and which converges towards therunning line at higher combustor mass flow rate {dot over (m)}.

FIG. 16 shows a schematic view of a method of controlling the gasturbine 100 according to an exemplary embodiment. Particularly, FIG. 16shows an example of the pilot split map, as described with reference toFIG. 15 , for acceleration scheduling during load acceptance due to apositive transient load change ΔL. As shown by the curved arrow in FIG.16 , during load acceptance due to the positive transient load changeΔL, the gas turbine 100 is controlled to move from the initial pilotfuel demand split on the running line, corresponding with the previouscombustor mass flow rate {dot over (m)}_(t-1) supplied in a previoustime step t−1, to operate at the new pilot fuel demand split between thesteady state combustor mass flow rate {dot over (m)} and the first pilotthreshold {dot over (m)}_(LBO) (i.e. a lower pilot fuel demand split),before returning to operate on the steady state combustor mass flow rate{dot over (m)} running line, following load acceptance. In this way, thegas turbine 100 may be controlled to operate closer to the first pilotthreshold {dot over (m)}_(LBO), allowing the gas turbine 100 to acceptlarger positive load changes ΔL without loss of pilot flame.

FIG. 17 shows a schematic view of a method of controlling the gasturbine 100 according to an exemplary embodiment. Particularly, FIG. 17shows an example of the pilot split map, as described with reference toFIG. 15 , for deceleration scheduling during load rejection due to anegative transient load change ΔL. As shown by the curved arrow in FIG.16 , during load rejection due to the negative transient load change ΔL,the gas turbine 100 is controlled to move from the initial pilot fueldemand split on the running line, corresponding with the previouscombustor mass flow rate {dot over (m)}_(t-1) supplied in a previoustime step t−1, to operate at the new pilot fuel demand split between thesteady state combustor mass flow rate {dot over (m)} and the secondpilot threshold {dot over (m)}_(TT) (i.e. a higher pilot fuel demandsplit), before returning to operate on the steady state combustor massflow rate {dot over (m)} running line, following load rejection. In thisway, the gas turbine 100 may be controlled to operate closer to thesecond pilot threshold {dot over (m)}_(TT), allowing the gas turbine 100to accept larger negative load changes ΔL without overheating of thepilot nozzle.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Tus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

The invention claimed is:
 1. A method of controlling a gas turbinearranged to supply a load, the gas turbine comprising a compressorarranged to operate at a rotational speed, a combustor and a fuel supplycomprising a first fuel supply and a second fuel supply, wherein thecompressor is arranged to supply air to the combustor at a combustor airmass flow rate and wherein the fuel supply is arranged to supply fuel ata total fuel mass flow rate to the combustor, the method comprising:detecting a load change to the load due to a transient of the gasturbine; and controlling the compressor, in response to the load changeand by way of a controller, to supply air to the combustor at a newcombustor air mass flow rate; wherein the new combustor air mass flowrate is within a range between a first threshold indicative of a leanblow out (LBO) limit and a second threshold indicative of a surge limit,wherein the controller comprises memory storing a first plurality ofrelationships to determine a correction factor for the load change tothe load, the memory further storing instructions to determine anallowable rate of change of the rotational speed for the load change tothe load, wherein the controlling by the controller of the compressor tosupply air to the combustor at the new combustor air mass flow ratecomprises the controller accessing the memory and processing the firstplurality of relationships to determine the correction factor andprocessing the instructions to determine the allowable rate of change ofthe rotational speed, wherein the controlling by the controller of thecompressor to supply air to the combustor at the new combustor air massflow rate is configured so that the new combustor air mass flow rate isbased, at least in part, on the determined correction factor and thedetermined allowable rate of change of the rotational speed.
 2. Themethod according to claim 1, wherein the first plurality ofrelationships includes a first relationship defined as follows:${CF} = \frac{{\overset{.}{\overset{\_}{m}}}_{TR} - {\overset{.}{\overset{\_}{m}}}_{SUR}}{{\overset{.}{\overset{\_}{m}}}_{SS} - {\overset{.}{\overset{\_}{m}}}_{SUR}}$wherein, CF represents the correction factor, {dot over (m)}_(TR)represents the new combustor air mass flow rate, {dot over (m)}_(SS)represents a steady state air mass flow rate, and {dot over (m)}_(SUR)represents the second threshold, wherein the correction factor CF iscalculated using the first relationship when the load change ispositive.
 3. The method according to claim 2, wherein the load change ispositive when {dot over (m)}_(TR)>({dot over (m)}_(SS)+Δ{dot over(m)}_(HIGH)), with Δ{dot over (m)}_(HIGH) being a fourth thresholdindicative of transient events, the fourth threshold being in a rangebetween the steady state {dot over (m)}_(SS) air mass flow rate and thesecond threshold {dot over (m)}_(SUR).
 4. The method according to claim1, wherein the first plurality of relationships includes a secondrelationship defined as follows:${CF} = \frac{{\overset{.}{\overset{\_}{m}}}_{LEO} - {\overset{.}{\overset{\_}{m}}}_{TR}}{{\overset{.}{\overset{\_}{m}}}_{LEO} - {\overset{.}{\overset{\_}{m}}}_{SS}}$wherein, CF represents the correction factor, {dot over (m)}_(TR)represents the new combustor air mass flow rate, {dot over (m)}_(LBO)represents the first threshold, and {dot over (m)}_(SS) represents asteady state air mass flow rate, wherein the correction factor CF iscalculated using the second relationship when the load change isnegative.
 5. The method according to claim 4, wherein the load change isnegative when {dot over (m)}_(TR)<({dot over (m)}_(SS)−Δ{dot over(m)}_(LOW)), with Δ{dot over (m)}_(LOW) being a third thresholdindicative of transient events, the third threshold being in a rangebetween the steady state air mass flow rate {dot over (m)}_(SS) and thefirst threshold {dot over (m)}_(LBO).
 6. The method according to claim1, wherein the controlling by the controller of the compressor to supplyair to the combustor at the new combustor air mass flow rate is furtherconfigured so that the new combustor air mass flow rate is based, atleast in part, on a product of the determined correction factor and thedetermined allowable rate of change of the rotational speed.
 7. Themethod according to claim 6, wherein the controlling by the controllerof the compressor to supply air to the combustor at the new combustorair mass flow rate is further configured so that the new combustor airmass flow rate is based on a sum of a determined actual rate of changeof the rotational speed and the product of the determined correctionfactor and the determined allowable rate of change of the rotationalspeed.
 8. The method according to claim 1, further comprising:responsive to the load change to the load, controlling the fuel supplyto supply to the combustor a proportion of the total fuel mass flow rateas a pilot fuel mass flow rate via the first fuel supply based, at leastin part, on a total combustor mass flow rate, wherein the totalcombustor mass flow rate is a sum of the combustor air mass flow rateand the total fuel mass flow rate to the combustor.
 9. The methodaccording to claim 8, wherein controlling the fuel supply to supply tothe combustor the proportion of the total fuel mass flow rate as thepilot fuel mass flow rate via the first fuel supply is based at least inpart, on a previous combustor mass flow rate computed in a previous timestep, wherein the previous combustor mass flow rate is obtained from aset of respective previous combustor mass flow rates.
 10. A tangiblenon-transient computer-readable storage medium for a controller of a gasturbine, wherein the gas turbine comprises a compressor arranged tooperate at a rotational speed, a combustor and a fuel supply, whereinthe compressor is arranged to supply air to the combustor at a combustorair mass flow rate and wherein the fuel supply is arranged to supplyfuel at a total fuel mass flow rate to the combustor, the tangiblenon-transient computer-readable storage medium having recordedinstructions thereon which, when executed by the controller, cause thecontroller to perform the following: control the compressor, in responseto a load change to a load of the gas turbine, to supply air to thecombustor at a new combustor air mass flow rate, wherein the newcombustor air mass flow rate is within a range between a first thresholdindicative of a lean blow out (LBO) limit and a second thresholdindicative of a surge limit, wherein the recorded instructions include afirst plurality of relationships to determine a correction factor forthe load change, the recorded instructions further configured todetermine an allowable rate of change of the rotational speed for theload change; process the first plurality of relationships to determinethe correction factor; process the instructions to determine theallowable rate of change of the rotational speed; and determine the newcombustor air mass flow rate based, at least in part, on the determinedcorrection factor and the determined allowable rate of change of therotational speed.
 11. A controller to control a gas turbine arranged tosupply a load, the gas turbine comprising a compressor arranged tooperate at a rotational speed, a combustor and a fuel supply, whereinthe compressor is arranged to supply air to the combustor at a combustorair mass flow rate and wherein the fuel supply is arranged to supplyfuel a total fuel mass flow rate to the combustor, wherein thecontroller is configured to: responsive to a load change to the load,control the compressor to supply air to the combustor at a new combustorair mass flow rate, wherein the new combustor air mass flow rate iswithin a range between a first threshold indicative of lean blow out(LBO) limit and a second threshold indicative of a surge limit, whereinthe controller comprises memory having stored thereon a first pluralityof relationships to determine a correction factor for the load change tothe load, the memory further having stored thereon instructions todetermine an allowable rate of change of the rotational speed for theload change to the load; access the memory to process the firstplurality of relationships to determine the correction factor and toprocess the instructions to determine the allowable rate of change ofthe rotational speed; and determine the new combustor air mass flow ratebased, at least in part, on the determined correction factor and thedetermined allowable rate of change of the rotational speed.